1. Field of the Invention
The present invention relates to method and instrument for measuring the contact angle of a rolling bearing. These method and instrument are useful for the easy, prompt and accurate determination of the contact angle of rolling elements with an outer raceway and an inner raceway in a rolling bearing.
2. Description of the Related Art
A variety of rolling bearings such as various ball bearings, for example, an angular ball bearing 1 shown in FIG. 5 or various roller bearings are assembled in bearing portions of various machines and apparatuses. Of these, the ball bearing 1 is constructed of an outer ring 3 having an outer raceway 3 on an inner peripheral wall thereof, an inner ring 5 having an inner raceway 4 on an outer peripheral wall thereof, and plural balls 6 disposed, as one type of rolling elements, for rotation between the outer raceway 2 and the inner raceway 4. Based on rolling of these balls 6, a member, such as a housing, with the outer ring 3 internally fitted thereon and supported thereon and another member, such as a shaft, with the outer ring 5 externally fitted and supported thereon are allowed to rotate relative to each other.
In such a ball bearing 1, a line a extending through the points of contact of each ball 6 with the outer raceway 2 and inner raceway 4 is tilted at an angle .alpha. with respect to a line b extending through the center of the ball 6 and the center of the ball 6 located at a position diametrically opposite to the former ball 6, so that the ball bearing 1 can bear not only radial loads but also axial loads. Since the angle .alpha. which is called the "contact angle" significantly affects the performance of the ball bearing 1, it is necessary to control the contact angle .alpha. at a desired value. In particular, high-performance ball bearings require strict control of the contact angle .alpha.. Although not illustrated by means of a drawing, the contact angle of rollers as rolling elements in a roller bearing must also be controlled strictly.
As will be described below, it has hence been practiced to determine the above contact angle .alpha. from the rotation angle .theta..sub.i of the outer ring 3 or inner ring 5 and the rotation angle .theta..sub.c of a retainer holding the balls 6 thereon [Japanese Patent Publication (Kokoku) No. 51-26824; Japanese Utility Model Application Laid-Open (Kokai) No. 52-143955].
To determine the contact angle .alpha. of the ball bearing 1 by the conventional method disclosed in the '824 publication, the determination is conducted as shown in FIG. 6. A drive shaft 9 is rotated by a motor 7 via a gear train 8. A coupling member 44 fixed on one end of the drive shaft 9 is fitted in an opening of the inner ring 5 at one side of the inner ring 5 (i.e., the upper side of the inner ring 5 as viewed in the drawing). Upon energization of the motor 7, the inner ring 5 rotates together with the drive shaft 9 and, at the same time, ! the revolution speed of the drive shaft 9 is detected by a rotary encoder 10 provided on an opposite end of the drive shaft 9. Namely, the rotation angle .theta..sub.i of the inner ring 5 is detected by the rotary encoder 10.
Further, a light-shielding plate 13 is mounted by way of a fixing arm 12 on an annular retainer 11 which rotatably holds the balls 6 (FIG. 5). Upon rotation of the retainer 11, the light-shielding plate 13 crosses between a light-emitting device 14 and a light-receiving device 15, said devices 14 and 15 making up a photoelectric switch. Because the retainer 11 rotates with revolution of the plural balls 6, the rotation angle .theta..sub.c of the retainer 11 with the balls 6 held thereon can be determined depending on how many times the light from the light-emitting device 14 to the light-receiving device 14 is shielded.
The contact angle .alpha. is then determined from the thus-determined rotation angles .theta..sub.i, .theta..sub.c, the outer diameter D.sub.a of the balls 6 and the pitch diameter d.sub.m of the balls 6 in accordance with the below-described formula. Incidentally, the outer diameter D.sub.a of the balls 6 and the pitch diameter d.sub.m of the balls 6 are dimensions which are determined upon manufacture. EQU .theta..sub.c =.theta..sub.i (1-D.sub.a cos .alpha./d.sub.m)/2
When the contact angle .alpha. of a rolling bearing such as ball bearing is determined by such a conventional method as described above, there is a limitation imposed on measurable rolling bearings. Moreover, the conventional method is not only unable to perform high-accuracy measurement but also difficult to permit automated measurement.
The imposition of a limitation on measurable rolling bearings is attributed to the following reasons (1) to (4).
(1) Because of the need for support of the light-shielding plate 13 on the retainer 11 via the fixing arm 12, it is impossible to measure the contact angle of any rolling bearing with a seal provided between the inner peripheral wall of the outer ring 3 and the outer peripheral wall of the inner ring 5. PA1 (2) In a small rolling bearing such as a small-diameter-ball bearing or miniature bearing, it is difficult to mount the fixing arm 12 on the retainer 11 so that measurement is practically impossible. PA1 (3) Measurement is not feasible where a rolling bearing has a structure preventing rotation of the fixing arm 12, for example, the outer ring 3 or inner ring 5 is provided with a flange. PA1 (4) In the case of a rolling bearing assembled in a machine or apparatus, rotation of the fixing arm 12 is often prevented due to an interference between the fixing arm 12 and another structure member or portion, thereby making it impossible to conduct the measurement in many instances. PA1 (5) The revolution angle of the balls 6 is first determined from the rotation angle .theta..sub.c of the retainer 11 on which the balls 6 are held, followed by the determination of the contact angle .alpha. from the revolution angle. There is, however, a slight play between the retainer 11 and each ball 6. Because of this slight play, it is impossible to obtain any accurate revolution angle. The contact angle .alpha. determined using the revolution angle is, therefore, not accurate. PA1 (6) As a result of the mounting of the fixing arm 12 and light-shielding plate 13 on the retainer 11, the inertial mass of the retainer 11 increases. The plural balls 6 held on the retainer 11, therefore, become susceptible to sliding against the outer raceway 2 and the inner raceway 4. When the balls 6 slide, an error also arises in the measurement value of the contact angle .alpha.. This also applies when sliding takes place between the inner ring 5 and the coupling member 44. PA1 (7) The fixing arm 12 must be connected at a basal end portion thereof to the retainer 11 to perform the measuring work. After completion of the measuring work, this fixing arm 12, then, has to be detached from the retainer 11. Such attachment and detachment work of the fixing arm 12 is cumbersome and must be conducted manually. This practically makes it impossible to add a measuring system, such as that shown in FIG. 6, in a manufacturing line for rolling bearings and to inspect the contact angle .alpha. of each rolling bearing manufactured through the line.
The unfeasibility of high-accuracy measurement can be attributed to the following reasons (5) to (6).
On the other hand, the difficulty in automating the measuring work is attributed to the following reasons (7).